Virtually all membranes can fuse, ranging from small intracellular vesicles and organelles to entire cells. Consequently, membrane fusion is critical for many biological processes such as fertilization, embryonic and postembryonic development, intracellular trafficking and viral infection (1-6). Exoplasmic cell fusion process involves the merger of plasma membranes. This process can be either transient, as in the case of sperm-egg fusion, resulting in a diploid cell that continues to divide, or permanent, resulting in the formation of syncytia multinuclear cells. Such syncytia serve as essential components of several somatic tissues in metazoans, including the myotubes in muscle formation, osteoclasts in bone formation and syncytial trophoblasts in the formation of the mammalian placenta. Exoplasmic cell fusion also takes place during specific viral infections, as enveloped viruses (such as, for example, influenza, HIV and rabies) fuse their membrane with the host's plasma or endosomal membrane. Similar to exoplasmic cell-cell fusion, viral-cell fusion takes place between the external layers of the fusing membranes and, as such, differs in many aspects from endoplasmic fusion events that occur within a cell (for example, vesicular membrane transport between organelles).
Existing models of the molecular mechanisms of membrane fusion rely on experimental and biophysical analyses performed mainly on viral and intercellular fusion-mediating proteins (known as fusogens). However, how well these models correspond to the mechanisms of action of cell-cell fusogens is unknown (4, 5). For example, U.S. Pat. No. 7,402,409 is directed to cell fusion method. Another cell fusion method is described, for example, by Gottesman et. al. (18).
AFF-1 (Anchor-cell Fusion Failure-1) and EFF-1 (Epithelial Fusion Failure-1) proteins from the nematode C. elegans are the first identified and therefore the founding members of a family of fusogens (that is, proteins mediating cell to cell fusion through fusion of the lipid bi-layers of the cells), conserved in nematodes (4). The C. elegans FF proteins (CeFF's) were shown to induce fusion in heterologous insect cells (for example, references 7-11). aff-1 and eff-1 mutants are viable, but have severe body deformities and reproductive defects associated with cell fusion failure (9,10). EFF-1's function as a fusogen requires its expression in both fusion partners (8). The Fusion Family (FF) family of proteins is very well conserved among nematodes. FF members were identified in various nematode species, suggesting that the FF family is conserved in the phylum Nematoda (4). Only a few members of the FF family have been identified outside nematodes, none of them in plants or in vertebrates.
Nematodes are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Over 28,000 Nematode species have been described (12) and about 16,000 of the nematodes are parasitic. The nematodes have adapted to nearly every, known ecosystem.
Infection by nematodes in general and parasitic nematodes in particular may affect various hosts, such as, for example, livestock, humans, marine habitats, plants, and the like (13), resulting in health-related and financial consequences. Thus, effective control of infection would contribute significantly to agriculture, farming and medicine with a resultant financial implication. For example, the World Health Organization estimates that at least two billion people are infected by parasitic nematodes, while damage by plant parasitic nematodes is estimated at ˜4-10 billion $ per year in losses in the U.S and over $80 billion per year in losses worldwide. Antinematodal agents (also known as antihelminthics, anhelmintics and vermicides), currently in use include mostly chemicals, pharmaceuticals or naturally occurring compounds that are designed to kill the parasite or expel it from its host. Nevertheless, most of these antinematodal agents are extremely toxic and if used in improper dosages are dangerous to humans. Furthermore, the continuous use of chemicals leads to the accumulation of resistant worms and inevitably to treatment failure. In addition, controlling pathogens such as parasitic nematodes can be extremely expensive.
Thus, there is an unmet need for new antihelminthic methods and compositions, that are specific, safe, non toxic, inexpensive and with minimal effect on the environment. The use of nematodal fusogens as exogenously expressed mediators for fusion of virus particles to cells or cell-cell fusion between cells of higher organisms of the plant and animal kingdom is neither taught nor suggested in the art.